Analog video signals define image data stored by the use of an analog modulation on an electrical signal. There are many established color analog video formats. One such color analog video system specifies the video image in terms of the luminance or luma (Y) and chrominance or chroma (C) of the image.
An analog video decoder can receive in a single channel or signal a color analog encoded video signal, for example, from a composite video input or from a television broadcast encoded analog signal. The luma and chroma components of the analog video signal can then be separated in such a way that they can then be presented on a screen or display.
Analog video is used in both consumer and professional applications and is found in many terrestrial television broadcast systems. For example, composite video, a format of analog television picture (picture only) signals, contains all the required video information, including color, in a single line level signal. Composite video is sometimes known as CVBS (composite video broadcast signal). The composite signal is a composite of three source signals Y (luma), U and V (representing hue and saturation or chrominance). Composite video signals can be found, for example, in many standard formats such as NTSC (National Television System Committee), PAL (Phase Alternating Line), and SECAM (Sequential Color with Memory) as well as the various sub-standards of these standards such as PAL-M, PAL-N, NTSC443, PAL-60.
A typical analog video decoder receives the composite video signal and separates these into the three source signals. However, in order to apply correct color decoding techniques to separate the luma and chroma to produce the correct image output, detecting the correct mode and/or standard of the modulation/encoding allows a more efficient decoding operation to be performed. Some standards can, for example, be detected by their synchronization timings; however, some cannot. For example, the PAL and SECAM standards have closely matched color burst frequencies and synchronization timings.
Furthermore, determining the color burst position in CVBS is similarly important in accurate video mode detection; under poor broadcast conditions the color burst position can be located in positions other than the designated or expected position on the back porch region of the signal.